Electrode cleaning process



-No Drawing.

Patented Jan. 10, 1933' HERBERT S. WOODWARD, OF MORENCI, ARIZONA, ASSIGNOR TO PHELPS DODGE CORPORATION, OF MORENCI, ARIZONA, A CORPORATION OF NEW YORK ELECTRODE CLEANING PROCESS This invention relates to a process of cleaning the surface of lead or lead alloy electrodes by the use of soluble sulphides.

In carrying out this invention sulphides or their solutions are applied to the surface of lead or lead alloy electrodes to soften or loosen any oxide coating, precipitate, or scale sov that such coating, precipitate, or scale may be easily removed as by mechanically brushing the surfaces of the electrodes or flushing them with water. In this way clean electrode surfaces are produced so that the maximum efiiciency in the use of power for electrolysis and in the production of chemical changes in the electrolyte can be maintained.

When a scale is formed upon the surface of an anode or when an insulating film of gas is held between a scale upon the surface of the anode and the anode itself there will be a corresponding resistance to the passage of the electric current to the electrolyte, thus causing higher power consumption per unit of metal deposited. In order to obtain' maximum efficiency in the production of chemicaland electro-chemical reactions in the electrolyte and the economical use of power it is therefore very desirable that the anode surfaces be kept clean.

Heretofore lead or lead alloy electrodes used in electrolysis have been cleaned by heating or scraping the surfaces to remove the coating of oxide, scale and any other precipitate or deposit adhering to the electrodes. This is costly in labor and sometimes damages the electrodes. Also, irregular patches of non-conducting scale or the like are often left which cause correspondingly higher current densities on the clean areas from which it is difficult to absorb the gas as rapidly as it is evolved during the electrolytic process. The high current density on the clean areas results in higher voltage drop in the passage of the electric current to the electrolyte and therefore higher power consumption per unit of copper deposited.

Another objection which results because of higher current density areas on the anode is the deposition of rough copper opposite them on the cathode. Rough copper exposes more surface to attack by ferric sulphate present Application filed October 27, 1931. Serial No. 571,466.

in the electrolyte, thus causing some of the deposited copper to be converted into copper sulphate. The presence of this ferric sulphate at the cathode causes counter-electronlotive force opposing the passage of the current through the electrolyte, thus resulting in higher power consumption.

The present invention is especially useful for cleaning the lead and lead alloy electrodes that are used in the Well-known electrolytic process for recovering copper from ores. In this process of recovering copper from ores, ore containing cuprous sulphide, 01128, is crushed and treated with a solution of sulphuric acid and ferric sulphate to dissolve the cuprous sulphide. The presence of other substances, such as copper sulphate, ferrous sulphate and aluminum sulphate promotes various desirable chemical or electro-chemical reactions or more economical operation of the electrolytic process. When the cuprous sulphide or chalcocite is dissolved from the ore ferric sulphate is converted into ferrous sulphate, thus Cu S 2Fe (S0 3 2CuSO +4FeSO S During the electrolytic recovery of the copper the following reactions probably take place as copper is deposited on the cathode and ferrous sulphate is converted into ferric sulphate:

The free oxygen is evolved at the anode and ferrous sulphate should be in contact with the anode to absorb the oxygen while it is desired is to enable the ferrous sulphate to come into intimate contact with the anode Where the SO radical of the copper sulphate is liberated, thus forming ferric sulphate from the ferrous sulphate.

An electrolytic process of the sort described above has been known for a long time and it has also been known that the success of this process depends largely upon the use of clean electrodes.

By the present invention the scale or precipitate can be easily and effectively removed from the electrodes, and especially from anodes of lead or lead alloy by first treating them with a solution of a soluble sulphide, such as sodium sulphide, ammonium sulphide, calcium polysulphide, hydrogen sulphides, or sulphides of alkalis and alkaline earth metals. By treating the anode With a soluble sulphide the lead peroxide, PbO which forms the scale, is chemically reacted upon and softened so that it can be easily removed by brushing or washing it off of the anode. The brushing or washing after the lead peroxide scale has been softened also removes other precipitates or mechanically deposited matter from the surfaces of the electrodes.

The electrodes may be treated with the soluble sulphides by placing a solution of one or more of them in a lead-lined tank, for example, and agitating the solution. The agitation may be easily effected by means of air jets at the bottom of the tank or in any other suitable manner. For example, an aqueous solution of chemically pure sodium sulphide, Na s, or commercial sodium sulphide (60 62%, Na- S) may be used in any convenient concentration. The stronger the concentration is the less time Will be required for the treatment. A concentration between 4% and 8% of sodium sulphide in Water has been found to be very satisfactory. The presence of inert materials or impurities in the solution appears to be permissible, and the temperature used may be ordinary room temperature or temperatures above or below this. The following equation indicates the reaction which takes place: 4NA S+4PbO +4H O= 3PbS SNaOI-I PbSOi I claim:

1. The process which comprises treating an electrode containing lead with a soluble sulphide and then mechanically removing loosened scale.

The process which comprises treating an electrode having lead peroxide scale thereon with a soluble sulphide.

3. The process which comprises treating an electrode having lead peroxide scale thereon With an alkaline sulphide.

4. The process which comprises treating an electrode having lead peroxide scale thereon with sodium sulphide.

HERBERT S. W0 ODWARD. 

